1. Field of the Invention
The present invention relates to substrate processing apparatuses, and more particularly to a substrate processing apparatus for supplying prescribed chemicals onto substrates (e.g., semiconductor wafers, glass substrates used as bases of liquid crystal displays, glass substrates for photomasks, substrates for optical disks, etc.).
2. Description of Related Art
As is well known, it is necessary in the process of manufacturing semiconductor apparatuses, liquid crystal displays, etc. to supply various chemicals (SOG, photoresist, developer, etchant, etc.) onto surfaces of such substrates as mentioned above. The aforementioned substrate processing apparatus is used for the supply of chemicals.
The substrate processing apparatus supplies chemicals onto the substrates using the same basic principles regardless of the type of the chemicals being used. That is to say, it drops a prescribed chemical in the vicinity of the center of rotation of a substrate rotating in the horizontal direction and causes it to spread all over the surface of the substrate by centrifugal force.
As an example of a substrate processing apparatus, an apparatus for supplying SOG (Spin On Glass, the apparatus is referred to as an SOG coater, hereinafter) will be described. FIG. 1 is a perspective view showing the entire structure of a conventional SOG coater. In FIG. 1, the SOG coater includes a wafer chuck 41 which holds by vacuum suction, for example a substrate (not shown) for rotatable movement about a rotation axis A (shown by the single dot line), a chemical dispensing nozzle 42 for dispensing a chemical onto the substrate surface, a nozzle arm 43 rotating around the rotation axis B (shown by the double-dot line) for placing the chemical dispense nozzle 42 in a prescribed position above the substrate, and a chemical introducing pipe 44 for introducing a chemical supplied from a chemical container (not shown) to the chemical dispense nozzle 42. The SOG coater also includes other structural elements, but they are not described and not shown in the drawing to clarify the invention.
In the aforementioned structure, a substrate is placed on the wafer chuck 41 by a transfer unit, not shown. The nozzle arm 43 places the chemical dispense nozzle 42 in a prescribed position above the substrate. Then the chemical introduced from an external chemical container is supplied to the chemical dispense nozzle 42 through the chemical introducing pipe 44. The chemical dispense nozzle 42 dispenses the chemical onto the substrate surface.
The SOG which is supplied onto the substrate surface by the SOG coater a chemical containing a silicon compound dissolved in a highly volatile organic solvent, such as alcohol, ester, ketone, or the like, which is mainly used for the purpose of planarizing interlayer insulating film formed on the substrate. SOG has the property of easily crystallizing at room temperature (about 23.degree. C.). Therefore, storing it at room temperature reduces its lifetime. Accordingly, when not used, the SOG is held in a chemical container and stored in a refrigerator (at a temperature of about 5.degree. C.) installed in a position separated from the substrate processing apparatus.
When using SOG, it is necessary to take out the chemical container of SOG from the refrigerator, expose it to room temperature until it attains the proper temperature for use (room temperature or thereabouts), and then place it in a prescribed position in the SOG coater. Since the SOG takes a long time to attain room temperature, substrate processing also requires a long time, thereby reducing the operating efficiency of the SOG coater. Furthermore, since the chemical container includes only the required amount of SOG for substrate processing, an operator must exchange the chemical container for every single substrate processing. This will increase the operator's work load, and consequently lowers the operator's work efficiency. Furthermore, when some SOG is left after substrate processing is finished, it must be discarded because it can not be used in the next substrate processing.
The aforementioned problems can be encountered not only with an SOG coater, but also with substrate processing apparatuses supplying other chemicals (photoresist, developer, etchant, etc.) onto substrate surfaces.